Electrolytic preparation of calcium d-arabonate



Patented Apr. 4, 1950 ELECTROLYTIC PREPARATION- OF' CALCIUM vD-ARABONATE Charles L. Mehltretter and William Dvonch;

Peoria, 111.,v assignors to the. United. States of America. as.represented by -the Secretary of Agriculture No Drawing. ApplicationAugust'9, 1946, SeriaLNo. 689,347

7 claims. (01. 204-49) (1Granted. .under. the act of Marchv 3', 1883, asamended April 30,. 1928; 370" 0. G. 757) 30,. 1928; and the inventionherein described, iiv

p'a-terited,v maybe manufactured and used by' or for the Government of'the United Statesor America for governmental purposes without thepayment to us ofany royalty thereon.

This invention relates to the preparation of calcium D-arabonate byelectrolytic oxidation of. solutions containing 2'-keto-D -gluconate. Itparticularly relates to-the preparation thereof by electrolyticallyoxidizing an aqueous solution of calcium. 2-keto-D-gluconate containing:abro"- mide, such as calcium bromide. It further re lates tooxidat'ionof liquors containing calcium Z-ketmD-gluconate, for example,fermentation liquors containing the latter.

'We have discovered that a yield of calcium D-arabonateas high as85percent canv be ob-. tained by the oxidation of an aqueous solutionofcalcium.v Z-keto-D-gluconate by bromine generated insolution. byelectrolysis of bromide; Good results-have alsobeen achieved bythedirect br o'-' mine oxidation of calcium 2-ireto-D-gluconate: in nearlyneutral. solution in the presence of car: bonate bufl'ers. However,the-advantage of the electrolytic process is that. considerably less.than one equivalent of calcium bromide can be-usedfor the oxidation.OfOIl'G'. equivalent of calcium 2r-keto-D-glu-conate. Also; the calciumbromide" is unchanged in:the: final mother liquor and can be used. fora-second oxidation; The. electrolysis.

occurs. in slightly acid solution and isrep'resentedf end of theelectrolysis'but the remainder appears as the solubleD-arabonolactone,which is formed along with an equivalent amount of calcium carb'onatewhichpreci'pitates out". The "arab'onolac tone isneutralized by heatingwith calcium car--- bonate. In the practice of this invention favorableresults are obtained when graphite electrodes aroused and the solutionis: mechanically stirred".

During thecourse' of the reaction, the reduc' ing value of the' mixtureis repeatedlydetermined with Fehlings' solution, and the electrolysisdisnote. the calcium D-arabonate formedcamba crystallized directly fromthe oxidation mixture" as practically pure calcium D-arabonate"pentahydrate; The final mother liquor which con-' tains the halide maybe used for asecond. oxidation by-simply adding more calcium 2-keto-D-gluconat'e' and repeating the process. ti'onliquors containing 'a highpercentage of calcium z-keto-D gluconat'e, such as that of Lockwoodet'alg U. S. Patent No. 2,277,716, were also oxidized by this processand gave good yields of calcium D-arabonate. In fact, it has been foundto be. more practical to electrolyze such liquors directly. It has alsobeen found that electrolysis at a temperature of 5 to 10 C. is conduciveto higher yields of. product, although satisfactory results are obtainedat 25 to 30 C. The following examples illustrate the nature of ourinvention:.

Example 1 60.0 grams (about A; mole) of calcium 2-ket0- D-gluconatetrihydrate and 8.0 grams of calcium bromide are dissolved in 1 liter ofwater in a 1500 m1. beaker containing two 3 x 7% x graphite electrodesplacedtwo inches apart. The solution which has a. pH of 6.4 is stirredmechanically and 1 ampere of direct current passed. through forapproximately 16.5 hours (theory is 13.4 ampere-hours) while maintainingthe temperature of. the reaction at 5 to 10'" C. and 'periodicallyreversing the polarity of the electrodes to remove the. cathodic depositthat forms. At the end of thistimathe solution has practically no.reducing value and-indicates substantially complete reaction of thecalcium 2-keto-D-gluconate. The oxidized. solution, containing calciumD-arabonate and D-arabonolactone, is heated with an excess of calciumcarbonate for two hours at to 100 C. to convert D- arabonolactonepresent to calcium D- arabonate and is filtered from excess calciumcarbonate. Upon concentrating the clear filtrate in vacuo, practi-'lcally pure calcium D-arabonate pentahydrate crystallizes outand iscollected on a filter and washed wit-1h per cent ethanol. Theair-driedproduct weights 43.1 grams which is a yield of 75"percentoftheory. Ithas a specific rotation: at. 25 C. of -3'.5 (C; 1.00;. H20)and. contains- 8.73 percent-calcium. Pure calcium D-arabonate has [a] 3=-3.0 (0,100; H20) and itscalcium; content is. 8.71. percent.

The mother liquor which: contains 5.8 grams of dissolved calciumD-arabonate and all of:

the. calcium bromide may be treated: with rnore calcium.2--keto-.l3'-glucona'te and the electrolysis Fermenta- Example 2 60.0grams of calcium 2-keto-D-gluconate trihydrate and 8.0 grams of calciumbromide are dissolved in one liter of water in a 1500 ml. f

beaker containing graphite electrodes. The solution is stirredmechanically and one ampere of direct current passed through for 13.4amperehours at a reaction temperature of 25 to 30 C. The electrolysisliquor is heated at 90 to 100 for two hours with excess calciumcarbonate and unreacted calcium carbonate removed by filtration. Theclear filtrate is concentrated in vacuo to a syrup which, on reactionwith excess hydrated lime, precipitates -;basic' calcium D- arabonate.The filtered basic salt is suspended in water with agitation andneutralized to phenolphthalein by the addition of carbon dioxide. Afterfiltering oil the precipitated calcium carbonate, the clear filtrate isconcentrated in vacuo to crystallize calcium D-arabonate pentahydrate.The filtered, washed, and air-dried product is obtained in a yield of 55percent of theory. At least 10 percent more is dissolved in the motherliquor so that the total amount of product formed-is 65 percent of thatrequired by theory.

' Example 3 Dextrose is fermented to 2-keto-D-gluconic acid withPseudomonas fluorescens in the presence of calcium carbonate. Ananalysis of the decolorized and filtered fermentation liquor indicatesthat 96 percent of the dextrose has been converted to calcium2-keto-D-gluconate. 406 ml. of clear liquor, containing 60.2 grams ofcalcium 2-keto-D-gluconate trihydrate, is diluted to one liter withdistilled water and 8.0 grams of calcium bromide added. This solution iselectrolytically oxidized at 5 to C. between graphite electrodes withthe aid of mechanical stirring. Electrolysis is continued for 17.5ampere-hours when the reducing value of the solution becomes negligibleand the pH' is 6.3.

The oxidized solution is heated on the steam bath.

Example 4 One-half of the final mother liquor of Example 3, whichcontains approximately four grams of calcium bromide, is mixed with 203ml. of fermentation liquor containing 30.1 grams of calciumZ-keto-D-gluconate trihydrate (about T 5 mole) and diluted to 500 ml.with distilled water.

Electrolysis of' this solution is carried out as illustrated in Example3 for 8.9 ampere-hours when a minimum of reduction of Fehlings reagent"occurs andthe solution reaches a pH of 6.3. The oxidation mixture isheated with excess calcium carbonate for two hours at 90 to 100 C. andfiltered. The clear colorless filtrate is concentrated in vacuo tocrystallization and nearly pure'i'calci'um D-arabonatepentahydrate isiso-x lated in a yield of 73 percent of that required by theory. Theproduct has a specific rotation at 25C. of -3.1 (C, 1.00;'H2O) andcontains 8.74 percent calcium.

The pH of the solution of calcium 2-keto-D- gluconate and calciumbromide used in Examples 1 and 2 was determined each time beforeelectrolysis and was found to be within the pH range 6.4 to 6.2. Thesevalues do not depart much from the pH of 5.4 that distilled water has inequilibrium with the carbon dioxide of the atmosphere. These values arein the range from about 6 to, but less than, 7.

Our process is carried out under weakly acid conditions. Electrolysis offree 2 keto D v gluconic acid did not yield arabonic acid.

Isbell, in United States Patent 1,976,731,

tion of vD-glucose can be oxidized electrolytically to calciumD-gluconate in nearly quantitative yield in the presence of bromide andcalcium carbonate. By prolonging the electrolysis to twice the periodrequired ,for conversion of D- glucose to calcium D-gluconate, Cook andMajor (J. Am. Chem. Soc. 57, 773 (1935)) have isolated calcium5-keto-Dgluconate in a yield of 9 percent. No other products'ofoxidation were reported. We have extended the time of electrolysis of anaqueous solution of calcium D- gluconate containing calcium bromide considerably beyond that reported by Cook and- Major and have obtained,besides calcium 5-keto- D-gluconate, the calcium salts of oxalic andD-arabonic acid.

A more detailed description of the electrolysis of calcium D-gluconateto calcium D-arabonate is given below.

A liter of an aqueous solution containing 28.1 grams of calciumgluconate monohydrate and 9.4 grams of calcium bromide dihydrate'waselectrolyzed between graphite electrodes. The solution was stirredmechanically and 0.5 ampere of current passed through for 26.8 hours at7.5 volts. It was then filtered from a small amount of cal-' ciumoxalate and concentrated in vacuo to 50 ml. After standing at roomtemperature for sev-' eral days 1.5 grams of calcium 5-keto-D-'gluconatecrystallized out and was removed by filtration. The filtrate was pouredinto 500 ml. of ethanol and the sirupy mass of mixed calcium salts thatformed, slowly crystallized. The crystalline material was filtered anddried in a desic-' cator over calcium chloride. The yield was 24.8grams. Five grams of this product was con densed with o-phenylenediam'ine by the method of Moore and Link (J. Biol. Chem. 133, 300 (1944)The filtered reaction mixture was made ammoniacal and after cooling at 5for several hours, 0.7 gram of crude arabobenzimidazole was obtained. Asecond crop of 0.24'gram was iso-'- lated from the mother liquor. Theyield of calcium D-arabonate was 17 per cent of that required by theory.

The electrolytic oxidation reaction involved in this invention requires,fo its best mode of op-;

eration, a certain minimum-amount of electri-' cal energy, and thisamount is determined by the amount of calcium Z-keto-D-gluconate being.

oxidized. The theoretical requirement is -ap-'-,

proximately 107 ampere-hours'per mole. In Example 1 of thespecification, one-eighth mole of calcium Z-keto-D-gluconate wasoxidized," and the theoretical amount of electrical energy was therefore13.4 ampere-hours. In Example 3 of" the specification, approximatelyon-eighthmole oi the salt was oxidized, the theoretical electricalenergy requirement being again 13.4 amperelifours. In Example 4,one-sixteenth mole was oizidized, the theoretical requirement being inthis case 6.7 ampere-hours.

Having thus described our invention, we claim:

1. The process for preparing calcium D-arabonate which comprisessubjecting an aqueous solution of calcium 2-keto-D-gluconate toelectjrolytic oxidation under slightly acid conditions in the presenceof calcium bromide in the proportion of less thanone equivalent perequivalent or; calcium 2-keto-D-gluconate and at a tempgrature of 5 to30 C. the electrolysis being disctintinued at the stage at which minimumreduction with Fehlings solution is reached.

3 2. A process of making calcium D-arabonate fii'om calcium2-keto-D-gluconate, comprising electrolytically oxidizing an aqueoussolution of calcium 2-keto-D-gluconate, the pH of the solution being inthe range from about 6 to, but less than; 7, in the presence of calciumbromide in the proportion of less than one equivalent thereof perequivalent of calcium 2-keto-D-gluconate at a temperature between about5 to 30 C., the electrolysis being continued up to and discontinued atthe stage at which minimum reduction with Fehlings solution is reached,treating the oxigllzed solution with calcium carbonate, separating thesolution, and subsequently concentrating to crystallize out calciumD-arabonate pentahydrate.

3. A process comprising electrolytically oxidizing an aqueous solutionof calcium 2-keto-D- "gluconate, the pH of the solution being in therange: from about 6 to, but less than, 7, in the presence of calciumbromide in the proportion of less than one equivalent thereof perequivalent of calcium 2-keto-D-gluconate, at a temperature between about5 to 30 C., the electrolysis being contirjiued for at least 13.4 amperehours per oneeighth mole of calcium 2-keto-D-gluconate and beings,continued no further than the stage at whichf minimum reduction withFehlings solution reached, and recovering calcium D-araf bonatje fromthe oxidized solution.

;keto-D-gluconate in the presence of a watersoluble bromide in solutionat a temperature in the range of about 5 to 30 C., the electrolysis be-,ing continued at least until calcium D-arabonate is" formed and for atleast about 107 amperej hours per mole of calcium Z-Keto-D-gluconate,

but no further than the stage at which minimum reduction with'Fehlingssolution is reached, and recovering the calcium D-arabonate from thesolution.

5. A process of making calcium D-arabonate from calcium2-keto-D-gluconate comprising {the stage at which minimum reduction withfFehlings solution is reached, and for at least the electrolysis beingcontinued no further than a about 13.4 ampere-hours per one-eighth moleof calcium Z-keto-D-gluconate.

' perature of 5 to 10, C.

6. The process of claim 5 operated at a tem- 7. The process ofclaim 5 inwhich the pH of the solution is in the range of about 6 to, but less fthan, 7 the electrodes being of graphite, and the .solution beingstirred during the electrolytic oxi- 'dation.

CHARLES L. MEHLTRETTER. WILLIAM DVONCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Isbell Oct. 16, 1934 Pasternack et al.Nov. 19, 1940 FOREIGN PATENTS Country Date Great Britain Jan. 21, 1932OTHER REFERENCES Industrial and Engineering Chemistry, vol 24, 1932, pp.375-378.

Bureau of Standards Journal of Research, vol.

6, pp. 1145-1152. Journal American Chemical Society, vol 57,

Number Number Transactions Electrochemical Society, vol. '74, 1938, pp.625-649.

1. THE PROCESS FOR PREPARING CALCIUM D-ARABONATE WHICH COMPRISESSUBJECTING AN AQUEOUS SOLUTION OF CALCIUM 2-KETO-D-GLUCONATE TOELECTROLYTIC OXIDATION UNDER SLIGHTLY ACID CONDITIONS IN THE PRESENCE OFCALCIUM BROMIDE IN THE PROPORTION OF LESS THAN ONE EQUIVALENT PEREQUIVALENT OF CALCIUM 2-KETO-D-GLUCONATE AND AT A TEMPERATURE OF 5* TO30*C. THE ELECTROLYSIS BEING DISCONTINUED AT THE STAGE AT WHICH MINIMUMREDUCTION WITH FEHLING''S SOLUTION IS REACHED.